THE CORRELATION BETWEEN CEREBROSPINAL-FLUID PRESSURE AND RETROLAMINARTISSUE PRESSURE

PURPOSE. TO measure the effects of cerebrospinal fluid pressure (CSFp) on retrolaminar tissue pressure (RLTp) and the translaminar pressure gradient (TLPG), particularly at low CSFp, which is the normal situati on in erect posture. METHODS. Micropipettes coupled to a servonull pre ssure system were passed into eyes of anesthetized dogs to the optic d isc and advanced in steps through the lamina cribrosa to the optic ner ve subarachnoid space (ONSAS), while pressure measurements were taken. Cerebrospinal fluid pressure and intraocular pressure (IOP) were moni tored and controlled. The TLPG was measured at varying IOPs and CSFps. The RLTp and ONSAS pressure (ONSASp) were measured at varying CSFps. In separate experiments, the optic nerve dura was incised, and pressur e measurements were taken across the pia mater. RESULTS. The TLPG was strongly correlated to the difference between IOP and CSFp (r = 0.93; n = 18) when CSFp was more than zero. Mean RLTp was 3.7 +/- 0.2 mm Hg (SEM; n = 15) when CSFp was 0 mm Hg. The ONSASp and RLTp were largely dependent on the presence of CSFp higher than break point pressures of -0.5 mm Hg and 1.33 mm Hg, respectively. However, below these break p oints, RLTp (slope 0.07) and ONSASp (slope 0.18) were little influence d by CSFp. Separate measurements across the pia mater revealed that 95 % of the pressure drop occurred within 100 mu m of the pial surface. C ONCLUSIONS. The TLPG and RLTp are dependent on CSFp when CSFp is more than -0.5 mm Hg. Below this level, there is no hydrostatic continuity between the intracranial and optic nerve subarachnoid space. In this r ange, RLTp is stable and is little influenced by CSFp changes.